Continuing the discussion from Replacing Mailing lists: Email-In:
My big concern is less about spam (this can be handled on the technical level and with moderators) and more about culture and habits - in the little time I have spent here on meta and experimented on discourse.kabissa.org, I have already seen that it can be incredibly hard to combine the two worlds. People simply think about email differently than they do forum posts, and the technical issues involved in making the user interface and functionality work more or less equivalently might simply not be worth it.
I see @codinghorror often making minor tweaks to my forum posts (thank you!) to clean up formatting and to move them to where they make sense. Today I sent an email in to my forum and even wrote it in a forum post style by editing heavily in gmail to make sure it’s comprehensible without reading down through the history of an email thread, but it still needed some editing after landing in the forum because the quotes didn’t transfer properly (first lines of all quoted text was not quoted in the post but was in the email).
So as discussed elsewhere on meta, the best approach to converting people over may be to just come up with a migration path for upgrading mailing lists that 1) moves everybody over to discourse groups with access to categories and 2) archives the mailing list and makes it read-only. Instead of spinning up a mailing list, we start a group and category, write the intro topic and then use the INVITE button there to invite people to join it.
This is a tall order and may take time, however, since it means convincing the folks who spin up a mailman list when they start a new project and those that are used to participating in mailing lists from the comfort of their own email client. In the meantime, the more we can do to ease the transition and bring in people who are used to mailing lists, the better. The welcome email, notification format, and web interface already go a long way to doing that… but there is likely more we can do to avoid freaking out the thousands of people we want to bring into discourse.